Coyote Cable has been experiencing an increase in cable service subscribers in recent months due to increased advertising and an influx of new residents to the region. The number of subscribers (in 1000's) for the last 16 months are as follows:

Month	Sales	Month	Sales	Month	Sales
1	12.8	7	20.6	12	23.8
2	14.6	8	18.5	13	25.1
3	15.2	9	19.9	14	24.7
4	16.1	10	23.6	15	26.5
5	15.8	11	24.2	16	28.9
6	17.2

Using simple linear regression, forecast the number of subscribers for months 17, 18, 19, and 20.